Since the cheeses and creams used in cheesecakes have such
a high moisture content, it is necessary to have an
ingredient that can hold or absorb water. The most
popular and the most elegant solution to this problem is
the egg. Also since egg yolks and whites harden as they
bake, they add body and texture to the cheesecake. Egg
yolks in particular contain lecithin, an emulsifier, which
has the effect of congealing the fats in the cheese.
Generally a cheesecake recipe with a high fat content will
also call for relatively more eggs.
Many recipes require you to separate the eggs and to beat
the whites until they form stiff peaks with the beaters of
your mixer. As egg whites are beaten, the albumen is spun
out into a finer and finer web of protein, the finer the
structure, the more moisture the batter can hold. If the
whites are overbeaten or overheated, however, the delicate
structure collapses and the result is a soggy cheesecake.
Since air is also encapsulated, the egg whites also add
lightness to the cake. Oddly enough, the freshest eggs
are not the best for cheesecakes; the whites of eggs that
are a few days old can be beaten to a larger volume.
Unless you have access to farm fresh eggs, though, this
isn't likely to be a problem as most of the store bought
eggs are already at least several days old.
When beating the egg whites, add a dash of cream of tartar
to make them more stable. To make the whites stiffer 9 if
this is desired) you can blend in some confectioners'
sugar or a boiling sugar syrup once the whites have
reached the soft peak stage.